The present invention relates to a fluid passage valve and a medical instrument which incorporates such a fluid passage.
Fluid transfusion sets are employed to transfer desired fluids from containers into patient's veins. The fluid transfusion set has a fluid passage valve, which is closed to avoid entry of air into the fluid when the fluid is introduced into a drip infusion tubular member.
One conventional fluid passage valve is shown in FIG. 1 of the accompanying drawings. The fluid passage valve, generally denoted at 2, is combined with a tubular body 6 which defines a constant-rate chamber 4 in a fluid transfusion set. The tubular body 6 has a bottom 8 in which a fluid passage port 10 is defined in the axial direction. The fluid passage port 10 has an open end communicating with the chamber 4 and surrounded by a circular ridge 12. A valve member 14 is separably placed on the ridge 12. The valve member 14 is enclosed by a casing 16 fused to the bottom 8, the casing 16 being of a rectangular vertical cross section. The casing 16 has a large opening or window 18 defined in a side wall 16a which extends perpendicularly to the bottom 8 The tubular body 6 has, on its top cover, a vent passage 20, a fluid inlet passage 22, and a mixture port 24.
When the constant-rate chamber 4 contains a fluid, the valve member 14 floats off the ridge 12 under its own buoyancy, opening the fluid passage port 10 to discharge the fluid from the chamber 4. When the fluid is discharged until its level reaches the bottom 8, the valve member 14 is seated on the ridge 12, closing the fluid passage port 10, so that no subsequent flow of air is permitted through the fluid passage port 10.
When the valve member 14 approaches the fluid passage port 10 as the fluid level is lowered, the edge of the valve member 14 tends to be caught by the side wall 16a of the casing 16. If the valve member 14 gets caught, it does not close the fluid passage port 10 even after the fluid is discharged to the level of the bottom 8, and air flows through the window 18 into the fluid passage port 10. The fluid passage valve 2 incorporated in the fluid transfusion set is therefore disadvantageous in that it allows air and the fluid to be supplied together.